The present invention relates generally to lasers employed in optical transmission systems and, more particularly, to current drivers for powering lasers in optical transmission systems.
Pump lasers are conventionally used in many different types of optical transmission systems. In such systems, pump lasers may, for example, be employed in fiber amplifiers (e.g., Raman amplifiers or erbium-doped fiber amplifiers) for amplifying input optical signals. As shown in FIG. 1, a conventional pump laser system 100 may include a laser diode LD 105 that is driven by a current driver 110. Fixed supply voltage Vt 115 further powers current driver 110. Inherent variations in the characteristics of each laser diode 105 used in pump laser system 100 can cause significant variations in the level of current and applied voltage that is required to produce a given optical output power.
Due to these inherent variations, the voltage level of fixed supply voltage Vt 115 is conventionally selected based on the least possible efficient laser diode 105 that may be used in pump laser system 100. Thus, for any given laser diode 105 used in pump laser system 100, current driver 110 adjusts the laser diode voltage VLD 120 to produce the current i 125 required by the laser diode 105 to output a specific optical power. Since supply voltage Vt 115 is fixed, the remaining voltage that is not dropped across laser diode 105 to produce the specific output power will be dropped across current driver 110. This voltage dropped across current driver 110 represents power that is wasted to produce a specific output power from laser diode 105. In practical laser systems, which may employ numerous laser diodes and associated current drivers, the multiplicative effect of this wasted power can be substantial, and may represent a significant portion of the power consumed by the overall system.
Therefore, there exists a need for systems and methods for reducing the quantity of power consumed by current drivers that drive optical transmission system laser diodes.
Systems and methods consistent with the present invention address this need and others by providing a current driver that includes current regulation circuitry for controlling each of the laser diodes of a series coupled laser diode pair. In one exemplary embodiment, at least one of the current regulators may increase or decrease the supply of current to one of the laser diodes by selectively diverting the current to a circuit path that may be connected in parallel to the respective laser diode. In other embodiments, one of the current regulators may adaptively control the voltage level of a power supply that powers both of the laser diodes. The power supply, thus, may supply only the minimum amount of voltage necessary to obtain a given optical output from the laser diodes. Operation of the current regulators, consistent with the present invention, advantageously serves to reduce the overall power consumed by the current driver as compared to conventional laser diode current drivers.
In accordance with the purpose of the invention as embodied and broadly described herein, a laser system includes first and second laser diodes coupled in series, and a power supply configured to adaptively adjust a voltage across the first and second laser diodes based on a current through at least one of the first and second laser diodes.
In another implementation consistent with the present invention, a laser system includes a power supply configured to supply current to a first laser diode, a first circuit path including the first laser diode, and a second circuit path configured to selectively divert current from the first circuit path to decrease the supply of current to the first laser diode.
In a further implementation consistent with the present invention, a laser system includes a series coupled laser diode pair, a first current regulator configured to control current supplied to the laser diode pair, a second current regulator configured to selectively divert a portion of the supplied current away from a first laser diode of the laser diode pair; and a power supply configured to adaptively adjust a level of a supply voltage applied across the series coupled laser diode pair.
In yet another implementation consistent with the present invention, a method of powering a laser system includes applying a supply voltage across first and second series coupled laser diodes, and adaptively adjusting a level of the supply voltage based on a current through at least one of the first and second laser diodes.
In a further implementation consistent with the present invention, a method of powering a laser system includes supplying a current to a first circuit path including a laser diode, and selectively diverting a portion of the current from the first circuit path to a second circuit path to decrease the current supplied to the laser diode.